obviously, someone has succeeded in using Stella to produce the projection on Coxeter planes of various 4D polytopes, including the omnitruncated 120-cell (333-Gidpixhi in Stella's database). See indeed this wikipedia page: https://commons.wikimedia.org/wiki/File ... 123_H3.png

After something like 45 minutes of searching for a way to do this in Stella, I give up and decided I should ask this forum.

This provide me lots of different projections, but I am not able to replicate the simple image for the 333-Gidpixhi I can find on Wikipedia, and neither am I able to get the other reflections. It is possible the author of that imagine has better knowledge of these Coxeter planes than I do and therefore knows which cell to select.

It's just a cell-first projection based on the truncated icosidodecahedron cells (green by default). So select one of those, use "View->Orientation->Look at Selected Cell..." to look down that axis, hide all the cells with Ctrl+Shift+H to only show edges/vertices, and of course hit "o" if you didn't already to use orthogonal projection.

That looks the same for me as on wikipedia, but slightly rotated around the axis out of the screen. You could line this up manually using Left+Right-drag or Middle-drag with the mouse.

I hid all but the green cells, and I tried with quite a few of the green cells. I attach here two trials. None were successful in getting me anywhere near the wikipedia image. I must be doing something wrong.

Hmm, not sure what's wrong. It doesn't matter which green cell you select. The important thing is to use "View->Orientation->Look at Selected Cell..." after selecting the cell, and then don't rotate the view again.